1. Field of the Invention
This invention relates to a slide fastener, and more particularly to a fastener stringer having a continuous plastic filament spirally formed and woven into an edge of a stringer tape during the weaving thereof by a needle loom.
2. Prior Art
There have been proposed a number of slide fasteners or zippers of the type described, which comprise a woven stringer tape and a plastic filament woven into a longitudinal edge of the tape, the filament being usually formed into a helical coil structure consisting of a succession of loops or elongated convolutions each having a coupling head, an upper and a lower leg and a connecting portion. A typical example of such fasteners is disclosed in German Application No. 2519829 wherein a preformed filament carrying a stiffening cord is inserted in the same manner as is the warp and interwoven with the weft into a longitudinal edge of a tape simultaneously as the latter is woven. Since the upper leg of each loop or convolution of the coiled filament in this prior art fastener stringer is not held in place by any weave thread, the result is that adjacent upper legs are prone to move out of the correct pitch, or the coupling filament on one stringer would often become disengaged from a corresponding filament on the other stringer when the fastener is subjected to bending stresses.
Another prior art example is disclosed in U.S. Pat. No. 3,921,679, wherein a warp thread is disposed over the upper legs of the coupling filament and interwoven in the spaces between adjacent filament loops with a weft thread. While this arrangement appears to provide secure anchorage of the coupling filament onto the tape, the warp thread extending over the filament tends to slip along the length of the loops and becomes shifted either toward the coupling head or the connecting portion under the influence of bends or twists, resulting in the failure to couple the two stringers and the breakage of the warp thread in frictional contact with the slider.
Still another prior art fastener stringer is disclosed in Japanese Laid-Open Publication No. 50-85445 wherein additional warp and weft threads are used for binding the coupling filament onto the tape, such threads being interwoven with the corefilled filament over the upper legs of the latter. The binding weft thread in this arrangement passes around externally of the connecting portions of the successive loops and hence extends laterally of the tape so far as to come into frictional engagement with the slider, which would in turn result in sluggish movement of the slider or torn tape threads.